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ABSTRACT
Homeowner's Handbook

to

Protecting Puget Sound Streams

Jan G. Tangen

Streams and groundwater of the greater Puget Sound Lowlands directly
feed the larger water bodies of the region, including Lake Washington,
Hood Canal, and Puget Sound itself. Therefore, stemming the flow of
pollutants into streams and groundwater, and ensuring adequate recharge
of groundwater, is vital to protecting the productivity of these ecologically
and economically important Puget Sound water bodies. Most pollutants of
Puget Sound streams are non point-sourced - meaning they cannot be
definitively tracked back to a single, or several, polluters. Instead, the
pollution comes as a result of a more difficult-to-control, amalgamation of
human-induced factors. Research shows the main antagonists for non­
point source pollution of water bodies in the Puget Sound region are
chemical fertilizers, storm water runoff, dysfunctional (and even
functional) septic systems, and urbanization of once rural areas. Indeed,
the Governor's 2005 Puget Sound Partnership found that reducing and
controlling non-point source pollution from these same antagonists to be
one of the most pressing issues regarding the clean-up and revitalization of
ailing Puget Sound. First understanding how these factors combine to
pollute the streams that feed Hood Canal and Puget Sound, and then
making some small investments and simple changes in the way we
manage the water that flows from our property into these streams and
groundwater, are significant steps toward alleviating the pressure of
urbanization and pollution on the health of Puget Sound and the greater
Puget Sound watershed. This paper surveys the ecological problems
created by urbanization and conventional stormwater management in the
Puget Sound region, and explores the feasibility of implementing
raingardens, pervious pavement, and native plantings to facilitate
stormwater runoff reduction and bioremediation.

Homeowner's Handbook
to
Protecting Puget Sound Streams

by
Jan G. Tangen

A Thesis

Submitted in partial fulfillment

of the requirements for the degree

Master of Environmental Study

The Evergreen State College

Olympia, Washington

June 2008

© 2008 by Jan G. Tangen. All rights reserved.

11


Contents

1.

Chapter 1
Introduction: Pollution, People & Puget Sound

2.

Roofs and Runoff

4.

Roots and Rain

5.

The Sub-surface and Salmon

6.

Septic Systems and Sea-life

6.

Picking Priorities

8.

Chapter 2
Bioswales, Buffers, Porousness and Plants

9.

Case Study: Street Edge Alternatives

13.

Case Study: Maplewood, MN

17.

Step By Step Raingarden

22.

Pervious Pavers and Percolation

24.

Non-Polluted Parking Lot

25.

Various Pervious Pavements

26.

Installing Permeable Pavement

28.

30.

Chapter 3
Septic Systems
Cost-effective Riparian Buffers

32.

Chapter 4
Conclusion

33.

References

37.

Appendix 1

IV

List of Figures

2.

Figure 1


3.

Figure 2


4.

Figure 3


5.

Figure 4


8.

Figure 5


10.

Figure 6


II.

Figure 7


12.

Figures 8 and 9


13 .

Figure 10


15.

Figure 11


16.

Figure 12


20.

Figures 13 and 14


23.

Figures 15 and 16


25 .

Figures 17, 18 and 19


26.

Figures 20 and 21


27.

Figure 22


28.

Figure 23


v

List of Tables

18.

Table 1


30. -

Table 2


Vi

Acknowledgements

Peter Dorman, Ph.D

Maria Bastaki, Ph.D

Sen. Dan Swecker


VB

1
Introduction:

Pollution, People & Puget Sound


Lake Sammamish

Washington State has become increasingly concerned about the water
quality and overall health of our economically and ecologically important fish­
bearing streams and the Puget Sound. In 2005, Gov. Gregoire created the 22­
member Puget Sound Partnership -a group of agency scientists and state leaders­
to investigate the reasons behind the pollution-caused problems throughout Puget
Sound (shellfish-harvesting closures, struggling wild salmon populations, and
Hood Canal eutrophication, for example) and then develop recommendations for
restoring it. A year later, the Partnership reported that human waste from on-site
septic systems is a main source of shellfish-harvesting bans, that highly polluted
creeks were contributing to the mortality of returning Coho salmon
(Oncorhynchus kisutch) before it manages to spawn, and that surface runoff has
in fact polluted nearly every water body in the Puget Sound Basin (PSP, 2007).

1


Recent research from the United States Environmental Protection
Agency has shown that once a drainage basin has had about 10% of its area
converted to impervious surface, the occurrences of habit-damaging flooding,
chemical and nutrient pollution, and the scouring of salmon eggs increase sharply
(EPA, 2008). Furthermore, one five-year survey of the greater Puget Sound basin
revealed that low and mid-lying drainage-areas below 2000 feet in altitude
showed a significant increase in impervious surface over this short time spansome as much as 19% (EPA, 2008).
With over 7 million inhabitants, and 2 million more projected by 2020, the
Puget Sound region is suffering from intense urbanization. This means more
roads, homes and concrete structures are being built in lowland areas that were
recently forest-covered or countryside, all without an addition ofland or
resources.
& Runoff

Impervious surface in Renton, during a rain event. Motor oil from surface runoff is a major non
point-source pollutant of Puget Sound streams.

Modem storm-water increases are a direct result of the roofs, gutters,
downspouts, curbs and roads of conventional storm-water management
infrastructure, which is designed to concentrate and move water away from where
it fell as quickly as possible. These systems compact the soil and result in

2


decreased porosity, further increasing the speed and volume of runoff (Landers,

2004).

Figure 2


ly
:m

Downtown Woodinville, after 2007 storm. Runoff is unable to infiltrate soil due to impervious
asphalt, and picks up hydrocarbon pollutants to deliver into nearby stream. Impervious surface
also heats runoff that enters streams, harming egg and salmon fry survival rates (EPA, 20081
Frazer, 2005)

:he

Surface runoff carries sediment, oil, chemicals, bacteria and other
nutrients across impervious surfaces such as rooftops and pavement, and delivers
them into streams and wetlands, rather than allowing for slow percolation and
filtration through the soil into the groundwater.
Roofs account for a very large portion of impervious surface area in
housing developments. They are designed to accumulate large volumes of water
in their gutters and whisk it rapidly away into the sewer system. This rapid runoff
can increase flooding and result in sewer overflows, and doesn't allow for any
groundwater replenishment (VanWoert, et. aI, 2005). Also, excessive surface
runoff has increased peak flow in streams, causing erosion and stream bank
instability (Bean, Hunt, Biddelspach, 2007)

ere

3


Figure 3

An example of lost vegetation and increased impervious surface at a golf course near Snoqualmie
Ridge, an area that was recently forest and wetland. Lawn is highly compacted, and grass roots
provide little nutrient and stormwater uptake.

Roots & Rain
A 1998 study comparing two neighboring catchments near Lake
Sammamish suggested the buffering effectiveness of deep roots in slowing runoff
velocity: it found that the forested (at the time) Novelty Hill Basin allowed only
12-30% of its annual rainfall to leave the basin as runoff, while the denuded
Klahanie Basin lost 44-48% of its rainfall to surface runoff. Even at a pervious
location in the Klahanie Basin, a simulated 50-year storm caused a peak runoff
flow 10 times higher than at the Novelty Hill site (Burges, 1998).
Another study conducted of a 1O-county region near Atlanta, Georgia
(which has experienced severe water-shortages in reservoirs in recent years),
found that the area had undergone a 20% loss in vegetation between 1986 and
1993, which resulted in an increase of 1 billion cubic feet of storm-water runoff
(American Forests, 1997).

4


The Sub-surface & Salmon

Pollution isn't the only danger to stream ecosystems brought by surface
runoff. Benthic invertebrates - relied upon by salmon :fry after emerging from
their gravel redds - have adapted to the subsurface flows of groundwater and
nutrients entering their streams, but the relatively sudden hydrological shift from
subsurface to surface flow has severely decreased B-IBI (benthic index of

lie

biological integrity - based on benthic macroinvertebrates) as urbanization
increases here (Morley, 2002). A survey demonstrated that only 10% of 45
stream-sites tested had healthy B-IBI. Along sockeye-bearing (0. nerka) Little
Bear Creek - in the quickly urbanizing Sammamish basin - high B-IBI occurred in

)ff

zones where native vegetation was prevalent, but was dramatically reduced
I

further downstream in more developed settings. Clearly, native riparian roots and
stormwater percolating deep into soil are vital to the biological health of a stream.

~~

Little Bear Creek, Sammamish Valley. According to Washington State Department of Ecology,
decreased groundwater levels have been found throughout Puget Sound, as well as increased
groundwater contamination. Groundwater flow into streams is decreased as surface runoff replaces
it, and increased volume and velocity of surface runoff inundating creeks results in creek bed
erosion and sediment deposition. This change in hydrology and velocity effects levels of sensitive
benthic invertebrates critical to salmon (Morley, 2002). Groundwater is also vital to sustaining
streams in dry periods.

f

5


Septic Systems & Sea-life
Of course, with an estimated half million residential septic tanks in the
Puget Sound region, much of the non point-source pollution making its way into
water bodies is in the form of human waste. According to Puget Sound
Partnership, nitrogen and phosphorus from septic and sewage-effluent is the
primary reason for shellfish-harvesting closures (PSP, 2007). This has not only
health impacts, but economic - as Washington is the country's number one
producer of shellfish. A study in Liberty Bay, on Hood Canal, found elevated
levels of coliform bacteria, a direct result of wastewater from leaking or otherwise
faulty septic systems. It also found high levels of phosphorus and nitrogen
nutrients (Takesue, et. aI, 2006), which can cause the algal population explosions
that lead to the recurring problem of eutrophication in Hood Canal. As the algae
eventually die and decay, bacteria suck up the available oxygen and choke out
marine species, creating "dead zones."

Picking Priorities
So with salmon populations, shellfish harvests, fresh water supplies, and
overall ecological health severely damaged by the conventional stormwater
management, impervious surfaces and septic systems of urbanization, it is not
surprising Puget Sound Partnership has allocated 24% of it's total budget
($76,831,744) to "prevent nutrient and pathogen pollution" from septic and
sewage systems, and 9% ($29,759,300) to "prevent harm from stormwater runoff'
(PSP, 2007).

6


But once individual homeowners understand these non point-source
pollution problems inherent to urbanization, they can apply cost-effective, easy­
to-implement strategies that help restore the ecological vitality and natural

)

hydrological system ofPuget Sound streams. This paper will explore the
effectiveness and practicality in the Puget Sound lowlands ofbio-retention cells
(or raingardens), native plantings, and porous pavement applied at a residential
scale.

lse

Ie

d

Jff'

7


2
Bioswales, Buffers,
Porousness and Plants:

Figure 5

Discovery Center, Seattle. A system of raingardens and porous pavers minimizes impervious
surface areas and limits the links between them, allowing stormwater to infiltrate the surface and
percolate within the sub-soil.

Increasing attention has been paid to Low Impact Development (LID)
techniques, as many regions attempt to undo the problems they've encountered
due to conventional storm-water management (Landers, 2004). LID techniques
attempt to restore natural hydrological functions, where rainfall and snowmelt is
absorbed and percolated back into the groundwater system or absorbed by roots,
and very little leaves the site as runoff.
The most familiar housing development type in the United States in
conventional curvilinear, with cul-de-sacs, large lots, and minimal open space

(Brander, et. aI, 2004). The most low-impact of development types is called
urban cluster. It is designed to maximize open space and use smaller lots. It

produces less runoff than any other type of development, as it retains more of the
natural features of the area.

8

A subdivision in Maryland was originally conceived as a traditional
housing development in 2002, but it instead incorporated LID standards without
increasing expenses: "fingerprinting" situated sites in such a way as to retain 50%
of the natural area, reducing the cost of clearing by $160,000, as well as the cost
of grading; 2 storm-water retention ponds were eliminated in favor of natural
drainage systems (saving $200,000 for the developer); replacing gutters and curbs
with swales reduced construction costs by $60,000; and narrower roads reduced
the price of paving by 175 (Landers, 2004).
Where soil conditions are favorable to percolation, on-site
filtration practices are quite effective and relatively inexpensive to implement
(Brander, et. aI, 2004). For example, improving water-infiltration on residential
property is far simpler than improving that of a parking lot. A good strategy is to
redirect runoff from impervious surfaces to more pervious ones. Runoff from
s

streets, driveways and sidewalks can be redirected into raingardens. These are

lS

sloped basins of highly-permeable soil atop natural subsoil. Preferably, the

s,

vegetation should be native so as to be well-suited to the area's climate and
hydrology. Roof downspouts can also be modified to spread runoff into vegetated
swales rather than into street-side drains (Brander, et. aI, 2004).

Case Study:
Street Edge Alternatives
In fact, natural drainage systems can cost 15-25% less than conventional
infrastructure redevelopment (Edwards, 2005). A pilot project along one street in
Seattle, Washington - dubbed "Street Edge Alternatives" (SEA) - showed the total

9


volume of water leaving the street was reduced by 98%! This was accomplished
with a redesigned street that reduced imperviousness by 11 %, along with the
addition of 100 trees and 1100 shrubs (Edwards, 2005).
Though no pervious pavement was used, a main goal was minimization of
impervious surface area. SEA redesigned the street into a narrower, curvilinear
path that allows for more porous surface area and keeps runoff from increasing in
volume and speed along the street. It added soil and native plants along the edges
of the road to help slow runoff and filter pollutants, and vegetated swales (broad,
shallow channels, densely planted with native vegetation adapted to the
precipitation and soil of the area) and stormwater cascades were constructed.
This allowed the ground to accept high volumes of runoff through staged
absorption.

2nd Av NW, Seattle. The re-designed, curvilinear street minimizes impervious surface, re-directs
street runoff into vegetated swales, and doesn't allow it to increase in volume and velocity. A
drawback of this type of decrease in impervious pavement may be the drastic reduction in
available parking along the street.

These cascades are a system of stepped pools alongside the street,
connected to one another by catch-basins. These pools collect and slow runoff on
its way down-gradient (Edwards, 2005; Landers, 2004). The system costs
$50,000 to $200,000 less per block to install than a conventional system with
large underground detention tanks (Landers, 2004).

The new trees and shrubs also provided evapotranspiration - not just

d

filtration and aeration, and excavated soils were mixed with organic compost to
reduce plant maintenance.
of

III

;es
Retention swales collect and reduce runoff. When the weir is topped, runoff proceeds to the next
retention swale down, where it is collected and reduced until it tops the weir again, and so on until
very little remains at the bottom of the system.

1,

This sort of "green infrastructure" doesn't deteriorate over time like the
conventional system of pipes, gutters, grates and curbs. In fact, it becomes more
effective as trees and plants grow (Edwards, 2005). Further, it increases
aesthetics, reduces property flooding, and improves ground- and stream-water
quality by filtering out pollutants from runoff - although the presence of
remaining street pollutants (like motor oil and trace elements) after percolation
through the soil remains to be studied (Lubick, 2001).
:cts

660 feet of 2nd Av, NW were retrofitted in this LID project that
successfully eliminated the flooding and erosion in Piper's Creek by mimicking
pre-development hydrological patterns - at the bargain-basement price of
$300,000 per block (Lubick, 2001).

on

11


Vegetated bio-swales retain runoff and filter pollutants through bioremediation as stormwater
percolates through the well-aerated soil.
Figure 9

Vine maple (Acer circinatum). The roots of native plants aerate the soil, allowing for recharge of
groundwater, and the bioremediation of pollutants. They are adapted to Pacific Northwest
climatic and precipitation patterns, and therefore require little maintenance and watering. They
also provide local streams with the appropriate allochthonous inputs important to salmon fry
growth.

The design achieved 100% retention by the final swale in 14 of 36
precipitation events, according to a study from July 2000 to January 2001
(Homer, et. aI, 2002). During dry periods, a full 78% of the runoff entering the
system was retained or otherwise infiltrated into the soil within the swales, and
38% over all periods. 38% retention/infiltration is good, but in comparison to the
previous drainage ditch it is outstanding: under the same condition, the old ditch
would have retained/infiltrated 67% less than the new system managed. It is
estimated the new curvilinear street design achieved a 42% reduction in runoff
from the previous street design. It is also estimated that pollutant loadings are

12


reduced by at least that same amount, if not more due to bioremediation provided
by the native plants within the swales (Homer, et. aI, 2002).
Apparently, the design achieved the best results in rains of moderate
intensity. Since this is the prevailing pattern in Seattle, the system is well-suited.
The previous conduit that was replaced by the cascade design would have
released approximately 191000 cubic ft more runoff into Piper's Creek than the
new system during the 2001-2002 wet season. Furthermore, SEA prevented
discharge of runoff into Piper's Creek 100% during the dry season, 98% during
the wet season, and reduced velocity by 20% (Homer, et. aI, 2002).

Case Study:

Maplewood, Minnesota


of

Runoff has easy access to this bioretention cell, a gently sloped basin capable of retaining and
draining most of the runoff from the lawn and nearby road.

the

Maplewood, MN, a suburb of the Twin Cities with a population of

h

approximately 30,000, was forced to implement raingardens due to a lack of
adequate space to treat stormwater, and to inadequate sewage in the older
neighborhoods. With its enormous supply of freshwater lakes, and increasing
impervious development, Minnesota faces similar pollution threats to Puget

13


Sound, with our plethora of salmon-bearing freshwater streams in urbanized
settings.
Begun in 1996 as the Birmingham Pilot Project, the project now
encompasses at least 376 homes, 2 schools, and includes a nature center and a
5000 sq. ft "raingarden park". At least 231 raingardens have been created.
Its intent was to improve street drainage without harming the neighborhoods'
character, to bioremediate pollutants before they reach nearby lakes, and to
minimize the price of retrofitting. It was designed to keep rainfall on-site and
withstand a ten-year precipitation event (Larabee, 2004)
The raingardens are vegetated bioretention cells that not only capture and
reduce street runoff by infiltration and root uptake, but also break down
stormwater pollutants through aerobic remediation - although little work has been
done to quantify actual pollutant load (Larabee, 2004).
The original gardens were simply six inches of native topsoil and 3/4 to 4
inches of wood mulch, built a top a French drain, which was basically a vertical
perforated pipe covered in 12 inches of aggregate intended to contain and slowly
disperse stormwater beneath the soil. The early versions were deemed by the
Minnesota Pollution Control Agency to be an illegal type 5 well, while the
USEPA granted the city 2nd place nationally for Outstanding Municipal Storm
Water Program. Gardens were located at the lowest point of the boulevards to
capture runoff, as the streets were curbless and runoff sheeted from streets onto
boulevards, and swales were constructed to direct runoff into the gardens.
Driveways were graded so that runoff could flow from one raingarden down to

14


the next - similar to the SEA's cascade design. For driveways with negative
grades, a hump was constructed street side to prevent runoff from flowing down
the driveway and encroaching on private property: the new system was integrated
into the old system, as in SEA, especially for emergency overflows.
Figure 11:
Runoff

-~'47~~

ld
o

Runoff
29. 2004

Re nfall
101_

,4

•

II

=-

.

E

ly

II

\/ \
\
\

The blue line records runoff in a nearby "control" neighborhood, and the red line records runoff on
two single days for the town of Bumsville: one before raingarden construction and one after.
Despite a larger amount of rain on May 29,2004, compared to June 6, 2003 - before construction
began - runoff was reduced from 35,972 gallons to a mere 994 gallons. Most of the rain that fell
on the pilot area remained there, filtered by the roots of the raingarden plants, and percolating into
the groundwater system - a reduction in stormwater runoff of97.3%! The control site, as
expected, shows an increase in stormwater runoff on the day that received more rainfall.

)

15

The second Project - Harvester - was built in 1999, and did make use of
French drains in the design (which are generally intended to disperse water, not
retain it and allow it to infiltrate). Another advancement was the use of input and
output pipes: this allowed runoff easy access into the raingarden near the bottom
of the trench, but in cases of over-inundation, the runoff could forgo the
raingarden and exit through the higher output pipe (Larabee, 2004). Some
raingardens were also constructed with emergency output directly into a swale or
sewer.
Through six projects in all, the garden and curb designs improved and
adapted to account for the characteristics of streets, gradients and residential lot
situations of the varying neighborhoods, and maintenance has been minimal for
homeowners: weeding and watering in year 1, and replenishing mulch every 3-5
years. Woodchips used as mulch in the original projects have clogged outlets,
and some erosion has occurred where curbs open to allow street runoff to access
raingardens.

A Burnsville, MN raingarden strategically placed to collect down-slope runoff. Notice the curb
has been amended to allow the conventional system and the raingarden system to function
together.

16


Step by Step Raingarden:

1) Locate low points in the garden, the outer edge of a sloping property, or areas
where puddling occurs. This is where runoff tends to be carried, or where
compaction has made infiltration difficult. Low spots near downspouts are most

11

conducive to collecting roof runoff. A collection of smaller rain gardens
strategically located to handle specific runofflocales can keep a single, larger
raingarden from being overwhelmed by an inundation of stormwater.

)r

-avoid locating the rain garden near the leachfield of a septic system,
within 10 feet of a home's foundation, near underground utility lines or
pipes, on or near slopes steeper than a 15% grade, or within the root­
systems of large trees.
-avoid locating in clay-like soil, or soil with a high water-table: dig a 1 to

5

2 foot deep hole in the location under consideration, and observe if water
begins filling the hole. If so, the groundwater table is too high, and the

s

location is non-conducive to retention cells. Or if the soil can be easily
formed into a ball when wetted, it is clay-like and not conducive to
retention cells.
2) Choose areas with most penneable soil. Clays are compacted and do not
infiltrate well: excavating and in-filling with native, loamy soil and compost is
necessary to improve clay's percolation-potential. Loamy and sandy soils
infiltrate well.
Test for proper soil infiltration rate (Hinman, et. aI, 2007):
a) Fill 1 to 2 foot hole with water.

17

b) Measure amount of water filled in hole, in inches.

c) Time how long it takes for that amount to completely drain.

d) The amount of water filled in hole divided by the amount of time it took to

completely drain is the soil's infiltration rate (measured in inches per hour).

e) Ifthe infiltration rate is 0.1 inch per hour, the location is poorly suited to a rain

garden.

f) If the infiltration rate is 0.5 inlhr or better, this is well-draining soil and ideal for

a rain garden.

g) Between 0.25 and 0.5 inlhr is not ideal, but still conducive to a raingarden.

Infiltration may be slow during wet season, and result in standing water for brief

periods. Any properly located and maintained raingarden will never have standing

water for more than 48 hours.

3) Detennine size of rain garden. Table 1 is for a rain garden 18 inches deep total.

By increasing the depth in poor-draining soils, annual volume can be increased.


Table 1

-

Rain garden size
as percentage of
.
.
ImpervIOus
surface drainage
area

Annual volume
of water held in
rain garden with
poor-draining
soil

Annual volume
of water held in
rain garden with
well-draining
soil

10%

70%

99%

I
90%

20%

for

I
100%

I

!

!

99%

100%

I
80%

I
100%

100%

mg
..

(Hinman, et. aI, 2007) The
row explams that the newly mstalled ramgarden is to be about
10% the size of the impervious surface area it will be draining (such as a house root), it will
manage to hold 70% of the runoff generated by that inipervious surface over the course of a year
in poorly-draining soil. That is a major reduction in stormwater runoff. While in well-draining
soils, that same-sized raingarden will achieve almost 100% runoff retention over the course of the
year!

:al.

4) Sloping properties can benefit from a rain garden built into or supported by a
porous retaining wall, such as one constructed of stone or concrete blocks, that
allows water to collect and infiltrate the soil within the cell, and the excess to
weep through the wall and join the conventional runoff. This is complementary to
conventional systems. Runoff into the rain garden can be slowed on the way
through a system of small gravel pools or dams.
5) After designing the size and shape of the rain garden, excavate between 18 and
30 inches. Side-walls should be sloped, not vertical. Level the trench and then
churn the bottom 8 inches of the soil, being careful to avoid compaction.

19

During trench excavation in Maplewood, MN, the backhoe stayed on the road in order to avoid
compaction of the soil.

6) If intending to collect roofrunoff, divert downspout and direct it into rain
garden using buried PVC piping or a shallow, gravelly trench lined with native
plants. Connect perforated piping and lay it across bottom of excavated rain
garden, within a bed of clean gravel. If not diverting a roof downspout, but
simply allowing runoff to flow down gradient into raingarden, a short, graded
trench backfilled with clean gravel around a perforated pipe allows runoff easy
entrance and dispersal inside the rain garden.

Bayview High School, Whidbey Island. A building's downspout has been diverted into an
excavated basin, and a perforated pipe laid within to aid stormwater dispersal. Overflow access to
the street is provided. This basin is not as deep as generally recommended, nor was it backfilled
with course gravel.

20

7) Backfill with native soil/compost mix (about 65/35) no less than 6 inches from
top of trench, and level it. Collected runoff should be allowed to pond in the rain
garden.
8) Ensure that excess storm water has drainage access to the street. Again, the rain
garden is intended as a complementary system to the conventional system already
in place. Outlets constructed near the top of the trench allow as much storm water
as possible to infiltrate before any excess is drained out to the conventional
system.
9) To prevent erosion during overflow of rain garden, line upper edges and outlets
with layer of clean gravel.
10) Plant native species within and around the perimeter of the rain garden. Group
the plants in to "wetland" and "upland" categories: wet soil/moisture loving plants
should be located in the low area of the rain garden - the "wetland" area; plants
preferring well-drained soil should be located on the upper slope and perimeter of
the rain garden. Avoid species with deep, spreading roots (such as large trees) that
may hann piping and make maintenance difficult. Refer to the Native Plants chart
in Appendix 1 to select appropriate plants.
11) Spread 2 to 3 inches of mulch a top surface, and water well.
12) Most maintenance is needed in first 3 years, as raingarden establishes itself.
This includes:
-weeding, mulching, and cutting back dead material to promote growth.
-watering adequately in summer

:s to

21


-clearing excessive debris and sediment to avoid clogging.
13) Allow raingarden to grow and establish. It will become more effective every
year at taking up storm water and nutrients, aerating the soil, filtering pollutants,
and allowing groundwater recharge as roots and leaves spread.

Pervious Pavers & Percolation

Clearly, replacing actual impervious surface with something more porous
promotes groundwaterlsurfacewater interface. Concrete walkways and asphalt
driveways allow no infiltration. Replaced with pervious pavers and asphalt, rain
and snowmelt can pass through and be filtered of contaminants. Pervious
pavement is relatively new, and is at this point effective in limited uses (EPA,
1999). Constructed of coarse aggregate with interconnected voids intended to
create permeability, both porous pavement and porous concrete are installed a top
a layer of gravel and crushed stone which is intended to work as a storage
reservoir. This layer can be modified to accommodate the amount of rainfall
encountered on any particular parcel, and perforated pipes within the layer can
drain away excess water. Unfortunately, where porous pavement has replaced
conventional concrete and asphalt, it has had a 75% failure rate. Generally, this is
due to poor installation and upkeep, a lack of engineers experienced with the
technology, and use atop soils non-conducive to high infiltration. (EPA, 1999)

22


Figure 15

ry

:s,

Highpoint Neighborhood, Seattle. Open-graded aggregate porous asphalt allows hydrocarbons
like motor oil to be filtered aerobically below the surface through bioremediation, instead of
entering streams through surface runoff.

us

Porous pavement and asphalt has been shown to be an effective substitute
for conventional pavement and asphalt in limited uses, such as sidewalks,

m

driveways, and parking areas: a residential driveway seems to be quite well
suited.
Figure 16

op
..
.......

-~:----.....

"

'<:::"'2:::'
A porous walkway and driveway at a residence on Queen Anne Hill, Seattle. Implementing open­
jointed paving blocks to alleviate excessive runoff that was de-stabilizing a backyard slope.

A study on the east coast tested infiltration rates at 40 various pervious
pavement sites, and found infiltration nearly doubled when simulated
maintenance of sediment removal from surface was performed - from 4.9 cmlh to
8.6 cm/h - in one test group. But in another group situated in proximity to
unstable or disturbed soil, the infiltration rates were significantly lower. The
study concluded that maintenance and location are vital to high stormwater
infiltration through pervious pavement, and recommends: 1) maintenance by

23

removing top 13-18mm of sediment and within voids using a vacuum to keep
infiltration at top capacity; then backfilling the voids with sand to avoid
compaction. 2) locating a pervious pavement system within a stable watershed,
because fine sediment accumulation dramatically reduces surface infiltration
capacity (Bean, et. aI, 2007).

Non-Polluted Parking Lot
Brattebo, et. aI, 2003, King County, Washington, evaluated 4 different
penneable pavement systems (and one non-penneable, conventional asphalt as a
control) in a well-used parking lot in Renton after 6 years of usage, to see if the
pervious pavement was still effective and functional. The study tested for
structural stability, infiltration capacity, and water quality. It found virtually no
signs of wear, almost no runoffleaving sites, and pollution in infiltrated water
was greatly reduced: significantly lower levels of copper and zinc than the
asphalted areas; no motor oil

infiltrated water from any of the penneable sites,

while it was found in 89% of samples from the asphalted sites. All the penneable
pavement systems resulted in virtually no runoff during 15 distinct precipitation
events throughout November 2001, and throughout January, 2002, while runoff
from the asphalt control site closely followed precipitation rates during all 15
precipitation events.
The study's authors point out that the success of the systems in this locale
can be greatly attributed to the high-infiltration rate of the soil, and the typically
low-intensity rainfalls of the Pacific Northwest. While not mentioned in this

study, it can be assumed that the region's lack of a freeze-thaw cycle or excessive
snow-clearing may well suit the long term stability of the pavement system.

Various Pervious Pavements

a
Figure 18

Open-jointed paving blocks: ideal for heavy foot traffic

le
Plastic geocells: a non-compacting base that can be covered with sad or gravel.

25

Porous asphalt

Pervious concrete

Installing Permeable Pavement:
1) Ensure soil of area to be paved has high infiltration, similar to steps taken in

choosing appropriate locale for raingarden. Allow 3 foot buffer between bed-

bottom and top of water-table. Avoid slopes of greater than 5 degrees.

2) Excavate area to be paved 12-36 inches deep, with vertical walls.

2) Level soil, being careful not to compact bed.

3) Cover soil-bed with non-woven geo-textile to avoid soil clogging the course

aggregate overlay.

4) Place perforated piping atop soil bed for dispersal.

5) rnfill with 12-36 inches of 1.5 to 2 inch clean, course aggregate.

6) Apply choice of pervious pavement surface. Grids, blocks and geo-cells are

most recommended for residential installations.


26


A bed of clean aggregate provides structure and stability, and promotes aeration, stormwater
dispersal, and non-compaction for pervious surfaces.

27


3

Septic Systems
Due to increasing land use in once rural areas, and to the realizations that
traditional methods are contributing to eutrophication in Hood Canal and other
water bodies, once acceptable septic practices that focused on dispersal for
treatment are no longer adequate.
But with 500,000 Puget Sound homes attached to septic tanks, and
because septics are economical, last up to 30 years, and require no outside energy
to function, it is unlikely they will be phased out and replaced by expensive sewer
systems (Hallahan, 2002).
In the meantime, conscientious septic owners will have to rely on proper
maintenance and improved filtering technology. For many, though, improper
sight-location and too little space has made their septic systems the number one
emitter of pathogens into water bodies in the state.

First Compartment

Second Compartment

Newer septic systems in Puget Sound have 2 compartments. When wastewater enters, heavier
solids drop to the bottom of the compartment and become sludge, while lighter solids rise to the
top as scum. The liquid effluent undergoes anaerobic treatment by bacteria, and eventually
overflows into the second compartment when more wastewater is added to the tanle In
compartment 2, the same process occurs, until the liquid effluent is released through the outlet into

28


the gravelleachfield. In the leachfield it disperses and is further broken down through aerobic
processes and evapotranspiration.

The septic system's efficient design is over 100 years old. Unfortunately,
today's home uses more water, sits on comparatively tiny parcels ofland, and may
not be situated upon soil with adequate infiltration. For example, clay or bedrock
requires much larger leaching beds than those that are fit into the limited space
provided by the smaller lots of housing developments.
Septic systems installed in soil with a water-table close to the surface do
not function properly. One reason for this is wastewater from the septic tank is
supposed to be dispersed into the surrounding soil through perforated pipes,

y

where aerobic organisms continue to break down pathogens, viruses and parasites.
If the soil is saturated it can't filter the wastewater. The tank may also back up and
get clogged (Steinfield, 2002). This typically results from a failure to pump the
tank remove when the sludge has come within 12 inches of the output, or the
scum within 3 inches. Inundations of wastewater into the tank can cause leaks as
well. Unfortunately, a study in Ohio showed that residential septic education
programs are largely ineffective at developing good septic-management practices
(Silverman, et. aI, 2005).
Of course, even a well-maintained tank releases effluent that can make it's
way into Puget Sound or its streams. As chemical additives have been proven
ineffective at increasing the microbial populations inside the tank that break down
the effluent (Pradhan, et. aI, 2008), responsible septic owners are left to invest in
expensive effluent-filters.

Ito

29


A simple effluent filter can be attached to the outlet of a conventional
tank, to catch effluent before it enters the leaching bed. It is relatively easy to
install and maintain, and costs around $300. Effluent filters reportedly reduce
Total Suspended Solids (TSS) 50-60%, and 5-day biochemical oxygen demand
(BOD) by 30-60%. Other systems have more integrated filtration, like
manufactured foam balls that ensure aerobic conditions during effluent filtration
before dispersal into the leaching bed (this is the Waterloo Biofilter). This
achieves a 90-95% reduction in TSS and BOD, as well as 95-99% reduction in
total coliforrns and 20-50% in total nitrogen! Unfortunately, installing this system
costs well over $1 O,OOO! Another uses a peat filtering system and achieves
similar results for a cost of $9000, plus total peat replacement every 8 years.

Cost-effective Riparian Buffers
It turns out, riparian buffers are more cost-effective than septic-upgrades

in reducing phosphorus pollution in NW lakes and streams in most every case
(Kramer, et. aI, 2006). Moreover, vegetated buffers can reduce phosphorus input
without actually pinpointing the source. A statistically analysis tested the cost­
effectiveness of two different strategies for reducing phosphorus pollution in 25
Minnesotan lakes spanning a broad range of characteristics and development ­
septic system upgrades, versus riparian buffers - and found riparian buffers to be
the best option for reducing sedimentary phosphorus input to acceptable
standards. The study assumed at $400/acre establishment cost for vegetated
buffers, and $20 annually for maintenance in 1996. Of the 25 lakes, 16 met the

30


phosphorus-loading reduction criteria using 15-61m wide vegetated buffers
encircling the lake, at a cost as low as $8476. 7 met the criteria using septic
upgrades alone, at a minimum cost (depending on lake size and amount of septic
systems) of$62,500. For 6 lakes that did not meet the criteria for phosphorus
reductions, the authors believe a combination of the septic upgrades and riparian
buffers would have been necessary. When the study ran another simulation that
assumed the main culprits of the phosphorus inputs were septic systems - rather
than a range that included rain falling directly on the lakes, lawn runoff,
pasturelands and agriculture - 15 met the criteria using riparian buffers alone, and

1

10 using septic upgrades alone. In each simulation, the authors found it was
possible to reduce phosphorus loading below the threshold in a greater number of
lakes using only buffer zones than using only septic upgrades.
Table: 2

Upgrade
type

Installation
cost

Conventional
tank
w/mound
Sand/peat
filter
Aerobic tank

$4000­
12000

Holding tank
Municipal
sewer

$5000­
$15000
$4000­
$7500
$2000­
$3000
$4000­
$10000

Annual
maintenance
cost
$80-$500

25-year cost

$12900

$500-$1000

$22000

$600-$1700

$28,750

$2000­
$3000
$200-$400

$70,000
$13000

(Gustafson, 2002) Column 1 lIsts vanous expensIve upgrades to the conventIOnal septIc tank wIth
a trench which are intended to reduce phosphorus pollution. Research shows that investing in
native plants to filter phosphorus from septic effluent is far more affordable than these costly
upgrades that may not be more effective than roots and aeration.

31


4

Conclusion:
All the LID techniques and technologies discussed herein are growing in
popularity and implementation. It is my hope that after completing this Thesis,
the reader has a strong understanding of how the greater Puget Sound watershed
is degraded by surface runoff and non point-source pollution from stormwater
infrastructure, urbanization, and septic systems, and of how it can be revitalized
through the proper application of permeable surfaces, native plants, and
bioretention swales.
Though the 2 case studies evaluated community-wide, government­
sanctioned solutions, they serve as excellent examples of these LID techniques
from which individual homeowners can draw inspiration and understanding.
The Homeowner's Handbook to Protecting Puget Sound Streams is
intended to show the potential these fun, relatively inexpensive, and easy-to­
implement strategies has for improving the health of Puget Sound and our
community.

32


References

American Forests. "My kingdom for a tree. " Civil Engineering 67. 10 (Oct 1997):8
,"Eban Z., William F. Hunt, and David A. Biddelspach. "Field Survey of Permeable Pavement Surface
Infiltration Rates." Journal ofIrrigation and Drainage Engineering. 133.3 (2007): 249-255
Brander, Kent E. , Katherine E. Owen, and Kenneth W. Potter. "Modeled Impacts of Development Type on
Runoff Volume and Infiltration Performance." Journal of the American Water Resources Association 40.4
(2004):961
Brattebo, Benjamin 0 ., Derek B. Booth. "Long-term Stormwater Quantity and Quality Performance of
Pern1eable Pavement Surfaces." Center for Water and Watershed Studies, Dept. of Civil and Environmental
Engineering, University of Washington. Seattle (2003) . Retrieved May 18 from
http://depts. washington.edulcuwDn
Burges, Stephen 1., Mark S. Wigmosta, Jack M . Meena. "Hydrological Effects of Land-Use Change in a
Zero-Order Catchment." Journal of Hydrologic Engineering 3.2 (1998): 86-97
Collick, Amy S., Zachary M. Easton, Franco A. Montalto, Bin Gao, Young-Jin Kim, Laurence Day,
Tammo S. Steenhuis. "Hydrological Evaluation of Septic Disposal Field Design in Sloping Terrains."
Journal of Environmental Engineering, 132.10 (2006): 1289-1297
Edmondson, W.T., and John T. Lehman. "The Effect of Changes in the Nutrient Income of Lake
Washington." Limnology and Oceanography 26.1 (1981): 1-29
Edwards, Amy. "In Seattle, When It Rains, It Drains - Naturally." Public Manager 34.3 (2005):61
Frazer, L. "Paving Paradise: The Peril ofImpervious Surfaces." Environmental Health Perspectives 113.7
(2005): 457-462
Gustafson, D.M., 1.L. Anderson, S.F. Heger, and B.W. Liukkonen. Choosing an alternative septic system
for a homesite with a high water table. University of Minnesota Extension Service, St. Paul, Minnesota,
2002
Hallahan, Dennis F. "The Standard Septic System: Still an Effective Choice for Onsite Wastewater
Treatment." Water Engineering and Management 149.10 (2002):33
Hinman, Curtis, Garry Anderson and Erica Guttman. Rain Garden Handbook for Western Washington
Homeowners. Washington State University, Pierce County Extension, 2007 . Retrieved June 2, 2008 from
http://www.pierce.wsu.edulWater_Quality/LIDlRaingarden_handbook. pdf
Homer, Richard R. , Heungkook Lim, Stephen J. Burges. "Hydrologic Monitoring of the SeattleUltra-Urban
Stormwater Management Project." Department of Civil and Environmental Engineering, University of
Washington, Seattle. Water Resources Series, Technical Report 170 (2002)
Hun-Dori s, Tara. "Advances in Porous Pavement." Stormwater: the Journal fo r Surface Water Quality
Professionals, (2005). Retrieved May 20, 2008 from: http ://www. forester.netlsw_0503_advances.html
Joy, Douglas, Claude Weil, Anna Crolla, & Shelly Bonte-Gelok. "New technologies for on-site domestic
and agricultural wastewater treatment." Canadian Journal of Civil Engineering, 28 (2008): 115-123

33


Kramer, Daniel Boyd, Stephen Polasky, Anthony Starfield, Brian Palik, Lynne Westphal, Stephanie
Snyder, Pamela Jakes, Rachel Hudson, Eric Gustafson. "A Comparison of Alternative Strategies for Cost­
Effective Water Quality Management in Lakes." Environmental Management.38.3, (2006): 411-425
Larabee, Erin. "Implementing rainwater gardens in urban stormwater management: lessons learned from
the city of Maplewood." Capstone project, Infrastructure Systems Engineering, 2004
Landers, Jay. "High-Impact Innovation." Civil Engineering 74.2 (Feb 2004):50
Lubick, Naomi. Environmental Science and Technology Online 40.19: 5832-5833 . Retrieved May 15, 2008
from http://pubs.acs.org/subscribe/journals/esthag/40/i19/htmI/100106tech.html
Moore, Jonathan W., Daniel E. Schindler, Mark D. Scheuerell, Danielle Smith, and Jonathan Frodge.
"Lake Eutrophication at the Urban Fringe, Seattle Region, USA." AMBIO 32.1 (2003): 13-18
Morley, Sarah, James R. Carr. "Assessing and Restoring the Health of Urban Streams in the Puget Sound
Basin". Conservation Biology 16.6 (2002): 1498-1509
National Resources Defense Council. Stormwater Strategies: Community Responses to Runoff Pollution.
Chapter 10: Strategies in the Pacific Northwest. Retrieved May 15, 2008 from
http://www.nrdc.org/water/pollution/storrn/chap IO.asp
Pradhan, S., Hoover, M.T. , Clark, G.H., Gumpertz, M., Wollum, A.G., Cobb, c., Strock, J. "Septic Tank
Additive Impacts on Microbial Populations." Journal of Environmental Health, 70.6 (2008)
Roberts, M.L. "Effects of Urbanization on Allochthonous Inputs to Small Puget Sound Lowland Streams."
American Geophysical Union, Spring Meeting 2005, abstract #NB22F-04, OS/2005
Puget Sound Partnership. 2007-2009 Puget Sound Conservation & Recovery Plan. Olympia: 2007
Silverman, Gary S. "The Effectiveness of Education as a Tool to Manage Onsite Septic Systems." Journal
of Environmental Health 68.1 (2005): 17
Snoonian, Deborah. "Drain It Right: Wetlands for Managing Runoff." Architectural Record 189.89
(2001):127
Stanley, Steven, Jenny Brown, and Susan Grigsby. Protecting Aquatic Ecosystems: A Guide for Puget
Sound Planners to Understand Watershed Processes. Washington State Department of Ecology, 2005
Steinfield, Carol. "Septic system Basics." Mother Earth News 194 (OctINov 2002)
Takesue, Renee, Jessie Lacy, Rick Dinicola, Ray Watts, Vivian Queija, Elisa Graffy, Dennis Rondorf,
Theresa Liedtke, Paul Hershberger. "Effects of Urbanization on Nearshore Ecosystemsin Puget Sound:
Liberty Bay Pilot Study". United States Geological Survey, NovlDec, 2006
United States Environmental Protection Agency. Office of Water. Storm Water Technology Fact Sheet:
Porous Pavement Washington: 1999. Retrieved May 2,2008 from www.epa.gov
United States Environmental Protection Agency. Region 10. Puget Sound Georgia Basin Ecosystem.
Retrieved June I from http://www.epa.gov/regionl O/psgb/indicators/urbaniz
change/what!
WSDOE. Washington State Department of Ecology. Retrieved Nov. 5,2007 from
www.ecy.wa.gov/puget_soundlindex.html

34


References

Figures and Tables


Cover: http://www.panoramio.comlphotos/original/1969149.jpg. retr. May 15,2008
Figure 1: Tangen, Jan (2008)
Figure 2: http://picasaweb.google.com/BlueFrog4191F100dingiphoto#5140571750782641170, retr. May 15,
2008
Figure 3: http://www.redmondinn.comlimages/attractions-golf4.jpg. retr. May 15,2008
Figure 4: http://www.1rboi.comlnrd/img/bear-creek-beforel.jpg. retr. May 15, 2008
Figure 5: http://mayflyeng.coml?Portfolio:Urban_Infill, retr. May 15,2008
Figure 6: http://seattlepi.nwsource.comllocal/95881_modeI20.shtml, retr. May 15, 2008
Figure 7: http://www2.seattle.gov/util/tours/ll0thCascade/slide3.htm. retr. May 15,2008
Figure 8: http://www2.cityofseattle.net/utilltours/seastreet/slidel.htm. retr. May 15, 2008
Figure 9: net/imagesl www.woodbrookRoNl.JPG, retr. May 15,2008
Figure 10: http://www.metrocounci1.orgienvironment/WaterSupply/images/raingardensmjpg, retr. May 15,
2008
Figure 11: http://www.1andandwater.comlfeatures/voI48n05/voI48n05 _ 2.php, retr. May 15, 2008
Figure 12: http://www.1andandwater.comlfeatures/voI48n05/voI48n05_2.php, retr. May 15, 2008
Figure 13 : http ://www.1andandwater.comlfeatures/voI48n05/voI48n05_2.php, retr. May 15, 2008
Figure 14: http ://www.whidbeycd.org/What.s%20New l .htm. retr. May 15, 2008
Figure 15: http://www.djc.comlnews/en/ll177213 .html. retr. May 15, 2008
Figure 16: http://www.inharmony.comlsherhart.html , retr. May 15, 2008
Figure 17: http://www.metaefficient.comlimages/ex3car.jpg. retr. May 15,2008
Figure 18:
http://www.ecofriend.orglimages/one_day
_may_be able_to_ collect_and
_rainwater.jpg&im
grefurl=http://www.ecofriend.orglentry/pavers-to-collect-purify-run-off-channeling-it-to-underground­
tanks-for­
reuse/&h=419&w=360&sz=47&hl=en&start=3&um=l&tbnid=qin4A8KOkIsBLM:&tbnh= 125&tbnw= 107
&prev=/images%3Fq%3Dporous%2Bpavers%26um%3D 1%26hl%3Den%26rls%3DHPIA,HPIA :2006­
36,HPIA:en%26sa%3DN, retr. May 15, 2008
Figure 19 : http://www.millennialliving.comlfiles/resizedphotos/porous-paver-system-driveway_ Ojpg, retr.
May 15, 2008
Figure 20: http://www.pavegreen.comlimages/water_image.jpg. retr. May 15, 2008

35

Figure 21: Yoders, Jeff. Retrieved June 7, 2008 from http://www.bdcnetwork.comJarticle/CA6297622.html
Figure 22: http ://www.tualatimiverkeepers.org/lid_website/paving.html. retr. May 15 , 2008
Figure 23:-http://www.metrokc.gov/health/wastewater/owners/works.htm, retr.

15,2008

Table 1: Hinman, Curtis, Garry Anderson and Erica Guttman. Rain Garden Handbook for Western
Washington Homeowners. Washington State University, Pierce County Extension, 2007. Retrieved June
2, 2008 from http://www.pierce.wsu.edu/Water_Quality/LIDlRaingarden_ handbook.pdf
Table 2: Gustafson, D.M., lL. Anderson, S.F. Heger, and B.W. Liukkonen. Choosing an alternative septic
system for a homesite with a high water table. University of Minnesota Extension Service, St. Paul,
Minnesota, 2002
Appendix 1: http://dm.metrokc.gov/wlr/pi/go-native/, retr. May 15, 2008

36


Appendix 1

_ All species listed are drought-tolerant, well-adapted to typical Puget Sound
climatic pattern of wet winters and dry summers. This list is only partial.

Native Species: Large Trees
Soil
Moisture
moist to dry

Light
Requirements
sun to shade

Notes

Big leaf maple
Acer
macrophyllum

moist to dry

sun

erOSIOn
control

Douglas fir
Pseudotsuga
menzlelsll

any soil
besides very
moist

sun to shade

ubiquitous

Red alder
Alnus rubra

moist to dry

sun to part
shade

fix nitrogen;
provide
filtered light

Shore pine
Pinus contorta

dry to very
moist soil

sun to part
shade

groups,
rows,
hedges

Garry Oak
Quercus
garryana

dry

sun to partial
shade

provide
filtered light

Western
hemlock
Tsuga
heterophylla

moist to wet
soil
preferred

part shade to
deep shade

tolerates
even full
sun well

Species

Grand fir
Abies grandies

stabilize
slopes

37


Sitka spruce
Picea
sitchensis

moist to very
moist

sun to part
shade.

damp areas

Western red
cedar
Thuja plicata

moist to very
moist

partial to full
shade

damp areas;
keep off
slopes

Native Species: Smaller Trees and Shrubs
Paper birch
Betula
papyrifera

moist

sun to partial
shade

Indian plum
Oemleria
cerasiformis

dry to moist

shade only

Bald-hip rose
Rosa
gymnocarpa

dry to very
moist

sun to shade

Kinnikinnick
Arctostaphylos
uva-urSI

dry

sun to partial
shade

stabilize
slopes

Red-flowering
currant Ribes
sangumeum

dry to moist

sun to partial
shade

welldrained,
rocky,
sunny sites

Mock orange
(Philadelphus
lewisii

dry to moist

sun to partial
shade

hedge

growth up
to 90'

38


Serviceberry
(Amelanchier
alnifolia

dry to moist
soil

sun to full
shade

erosIOn
control

Snowberry
(Symphoricarpos
albus

dry to moist
soil

sun to full
shade

extremely
tolerant;
fast growth

Tall Oregon
grape (Mahonia
aquifolium

dry to very
moist

sun to full
shade

Red elderberry
Sambucus
racemosa

dry to moist

sun to shade

Goldenrod
Solidago
Canadensis

dry to moist

sun to partial
shade

Oregon ash
Fraximus
latifolia

moist to very
moist

sun to part
shade

Pacific ninebark
Physocarpus
capitatus

moist to very
moist

sun to shade

Vine maple
Acer circinatum

dry to moist

partial to full
shade

grouped

stabilize soil

39


Cascara
Rhammis
purshiana

moderately
moist

sun or shade

30' growth

Nootka rose
Rosa nootkana

moist to very
moist

sun to partial
shade

rapid spread

Black
cottonwood
Populus
balsamifera

very moist

sun to partial
sun

stabilize soil

Red osier
dogwood
Comus sericea

moist to very
moist

sun to partial
shade

very low
maintenance

Sword fern
Polystichum
munitum

Native Species: Ground Cover
dry to moist
partial to full
soil
shade only

Western
starflower
Trientalis
latifolia

dry to moist

partial to full
shade

Woodland
strawberry
Fragaria vesca

dry to moist

partial shade
to shade

Dagger-leaf
rush
Juncus
ensifolius

wet

sun to shade

erosIOn
control

rapid spread

40


Reed
mannagrass
(Glyceria
grandis

moist to very
moist

sun

meadows

Wild
strawberry
Fragaria
vlrgmlana

dry to moist

partial to full
shade

rapid spread

Lady fern
Athyrium
felix-femina

moist

sun to shade

stabilize soil

All pictures (http://dnr.metrokc.gov/wlr/pi/go-native/)

41